The present invention relates to a method of navigation and to a navigation method of updating the navigational information in an aircraft, and more particularly the invention relates to navigation which includes a sensor, signal processing devices and arrangement and a store for reference information.
Navigational methods of the kind to which the invention pertains usually operate as follows. An aircraft such as a regular airplane, a helicopter or any other kind of flying craft flies across a certain territory and scans the territory underneath. The scanning result is compared with reference data available in a suitable store in order to obtain nagivational and navigation correction. Aircraft usually employ a plurality of navigational systems. The basic system in an aircraft however is usually based on inertia, and that navigational system is supported either manually visually by the pilot or though telecommunication satellite range finding and so forth.
A variety of overflight navigational methods are known under names such as TERCOM, TERPROM, SITAN, SPARTAN, PENETRATE wherein the craft is located by scanning a territory strip across which the craft flies by means of radar in order to ascertain an elevational or range image. This scanning signal is digitized and compared with digitally available reference data of the same territory. One covers in one shot so to speak an area having several hundred meters length. An on board computer or the like compare the reference data with the acquired real time radar data. The reference data have been acquired originally by measuring elevation above a certain level and with reference to particular reference level. The scanned strip is then digitally compared with appropriate elevational digitized data. The Tercom method is for instance described in German Patent 3,016,901 which in turn refers to a paper in "Flight International", of 10/01/1977, pages 964/965. It is apparent that this kind of system works only if indeed there are significant elevational differences of a sufficiently pronounced nature for purposes of navigation; but whatever craft flies across flat areas, lakes or flat fields there simply is no or insufficiently pronounced information available which could be used for navigation. Clearly there are marginal areas with slight elevational differences but then one has to consider the margin of error and measuring tolerances.